Mobile communication devices are fast becoming ubiquitous. These devices commonly utilize one or more antenna systems to facilitate signal transmissions—both transmitting and receiving—with some wireless host system or network. Maximizing the strength and reliability of such transmissions is one common concern in antenna design. Ideally, an antenna of the highest possible power would, in most cases, provide optimal transmission performance.
Practically, however, there are several other design concerns that must be balanced against maximizing antenna power. Most mobile communications devices operate—at least partially—on battery power. Thus, in order to maximize battery life and be commercially viable, all components and sub-systems within a mobile communications device—including an antenna system—must utilize as little power as practical. Various regulatory and industry restrictions or standards limiting antenna system power levels must also be considered and addressed. For example, governmental regulations on SAR (specific absorption ratio) values can limit the amount of power with which an antenna system may transmit. Thus, mobile communications device designers and manufacturers must attempt to optimize antenna system performance within some limited range of operating conditions.
Although the performance of a given antenna system may thus be optimized from a design perspective, its actual performance while in use may be impacted by a number of operating environment variables. Physical barriers or obstructions, and sources of signal interference, can degrade antenna performance levels, and erode communications reliability. To a certain extent, some such deleterious conditions cannot be avoided or obviated. Consider, for example, the effects of a user's body components—particularly the hand and fingers—on the antenna performance of a wireless phone.
The proximity of a user's head, hand, fingers or other body component can significantly decrease antenna performance levels. Where a hand or fingers cover some or all of a mobile device antenna, absorption effects can attenuate transmitted or received signals. Close proximity of a body component to an antenna can also increase VSWR (voltage standing wave ratio) levels—decreasing antenna efficiency.
Conventionally, mobile station antenna systems do not change antenna configuration based upon proximity of some obstruction or interference source—particularly a user's body component. A number of systems simply accept or ignore such conditions. Some systems attempt to compensate by providing some form of tuning circuitry. Unfortunately, however, such approaches can add significant expense and commonly provide only suboptimal performance. Most conventional tuning circuitry is passive in nature, and designed to provide fixed compensation over some fixed range.
As a result, there is a need for a system that provides an adaptive antenna system in a mobile communications device that compensates for a wide range of actual operating conditions in an easy and cost-effective manner.